Estrogen conjugation and antibody binding interactions in surface plasmon resonance biosensing

Area of Science:

• Steroid chemistry
• Bioconjugation
• Biosensor development

Background:

• Estradiol immunoassays are crucial for clinical diagnostics.
• Developing sensitive and specific detection methods for estradiol is essential.
• Surface Plasmon Resonance (SPR) offers a label-free detection platform for biomolecular interactions.

Purpose of the Study:

• To synthesize novel thioether-linked 3-mercaptopropionic acid derivatives of 17beta-estradiol and estrone.
• To immobilize these derivatives onto carboxymethylated dextran-coated gold sensor surfaces for immunoassay development.
• To compare the antibody binding affinities of estradiol conjugates at different positions (2-, 3-, and 4-positions) and optimize an estradiol SPR immunoassay.

Main Methods:

• Synthesis of thioether-linked estradiol and estrone derivatives via substitution of 4-bromo analogues.
• Immobilization of estradiol-oligoethylene glycol (OEG) derivatives on SPR sensor chips.
• Surface Plasmon Resonance (SPR) analysis using a BIAcore instrument to measure antibody binding.
• Development of a secondary antibody-mediated signal enhancement for improved sensitivity.

Main Results:

• Estradiol conjugates at the 2- and 4-positions exhibited strong binding to monoclonal anti-estradiol antibody.
• The 3-conjugate, linked through the existing 3-OH group, showed significantly reduced antibody binding (2% compared to the 2-conjugate).
• An optimized SPR immunoassay using 2- and 4-position conjugates achieved a detection limit of 25 pg/mL with a 9.5-fold signal enhancement.

Conclusions:

• Conjugation site significantly impacts antibody binding affinity in estradiol immunoassays.
• Estradiol derivatives conjugated at non-functionalized positions (2- and 4-) are superior for antibody recognition.
• The developed SPR immunoassay provides a rapid, sensitive, and convenient method for estradiol detection.